Intra ocular lenses (IOLs) are surgically implantable lenses which replace or supplement optical function of the NCL. So called “posterior chamber intraocular lens”, or PC IOLs, replace the NCL in the case of cataract or, more recently, in the case of presbyopia by so called “clear lens exchange”, or CLE. Other implantable lenses are placed into the anterior chamber of the eye (AC IOLs), into the cornea (corneal or intrastromal implants) or between the NCL and iris (so called “implantable contact lens” or ICL). So far, most of these IOLs were designed to replace or to supplement the basic optical function of the NCL only. It should be appreciated that an NCL in a human eye, depicted in the FIG. 1, is a complicated structure with several functions. The main eye parts include the cornea 101; the iris 102; the NCL 103; the posterior capsule 104; the cilliary muscle 105; the zonules 106; the vitreous body 107; and the retina 108.
The basic optical function of the NCL 103 consists in helping the cornea 101 to focus the incoming light so that a distant object can be projected on the retina 108. The other important optical function is accommodation—adjustment of optical power of the lens in such a way that objects at various distances can be projected onto the retina 108. There are several theories explaining the accommodation mechanism. See for example L. Werner et al, Physiology of Accommodation and Presbyopia, ARQ. BRAS. OFTALMOL. 63(6), DEZEMBRO/2000-503.
The most firmly established theory is von Helmholtz theory explaining that, referring to the FIG. 1, relaxed cilliary muscle 105 causes tension in the zonules 106 that pull the lens 103 periphery outward to keep the NCL 103 in its deformed (flattened) shape that provides a lower refractive power suitable for distant vision. Focusing on a near object is caused by tension in the cilliary muscle 105 that relaxes the zonules 106 and allows the NCL 103 to obtain its “natural” configuration with a smaller diameter, larger central thickness and smaller radii of curvature on both anterior and posterior surfaces. This increases the NCL's refractive power and allows for projection of the image of near objects on the retina 108.
Most of the common intraocular lenses have spherical surfaces that can be manufactured rather readily. It has been assumed for some time that the NCL 103 is essentially spherical. However, a spherical lens is not exactly monofocal, instead it demonstrates so called “spherical aberration” wherein rays incoming through the center are bent into a focal point that is slightly further from the lens than rays incoming through the lens periphery. Therefore, a spherical lens is somewhat more refractive in its periphery than in its center. This change is continuous: such a lens does not have a single focal point, but many focal points in a short interval of distances (focal range) between the longest and shortest focal distance. In other words, a spherical lens is negatively polyfocal (its focal distance decreases from the center to the periphery). Lenses with elliptical rather than spherical surfaces (such as surfaces created by solidification of a static liquid meniscus) have even more distinct spherical aberration and are, therefore, even more negatively polyfocal than spherical lens.
Some artificial intraocular lenses include hyperbolic surfaces alongside with other surfaces of second order, such as spheric or even elliptic surfaces that have negative polyfocality and very opposite optical effect. More importantly, the prior art generally combines second order (or conic section) surfaces with meniscoid surfaces that are poorly defined and merely approximate second order surfaces with positive spherical aberration (although never surfaces with hyperbolic aberration).
For example, Wichterle in U.S. Pat. No. 4,971,732 claims the meniscoid surfaces to approximate a flat ellipsoid while Stoy in U.S. Pat. No. 5,674,283 considers meniscoid surfaces an approximation of a spherical surface, both having negative polyfocality. A combination of surfaces with positive and negative polyfocality diminishes or negates advantages of the former.
Furthermore, Wichterle '732 describes a manufacturing method of the intraocular lens where a monomer solidifies in an open mold, one (posterior) side of the lens having the shape of the mold cavity while the anterior side has a shape of a solidified liquid meniscus (presumably approximating a flat ellipsoid shape with negative polyfocality, being somewhere between purely spherical and purely ellipsoid surface). The mold cavity has the shape of a second order surface that may include a hyperbolic surface. One can note that each of the optical surfaces is created differently—one by solidification of a polymer precursor against a solid surface while the other by solidification on the liquid-gas interface. It is known to those skilled in the art that the surface quality of the two optical surfaces formed under such different circumstances may differ profoundly in both optical and biological respects.
Wichterle in U.S. Pat. No. 4,846,832 describes another manufacturing method of the intraocular lens where the posterior side of the lens has the shape of the solidified liquid meniscus (presumably approximating a flat ellipsoid shape with negative polyfocality) while the anterior side is formed as an imprint of the solid mold shaped as a second order surface that may implicitly include also a hyperbolic surface. Again, we can note that each of the optical surfaces is created differently—one by solidification of a polymer precursor against a solid surface while the other by solidification on the liquid-gas interface.
Stoy '283 discloses modifying the method described by Wichterle '732 using a two part mold, one part being similar to the Wichterle's mold while the other being used to form a modified meniscoid of a smaller diameter on the anterior lens surface. The meniscoid optical surface is of the same character as the meniscoid resulting from Wichterle '732, albeit of a smaller diameter and, therefore, probably closer to a spherical surface than an ellipsoid surface. In any case, such a surface has negative polyfocality. The posterior side is formed as an imprint of the solid mold shaped as a second order surface that may include a hyperbolic surface while the other optical surface is formed by solidification of the liquid polymer precursor on the liquid-gas interface.
Michalek and Vacik in PCT/CZ2005/000093 describe an IOL manufacturing method using a spin-casting method in open molds. Molds filled with monomer mixture spin along their vertical axis while polymerization proceeds. One of the optical surfaces is created as the imprint of a solid mold surface while the other is formed by the mold rotation. The imprinted surface has the shape formed by rotation of the conic section along the vertical axis (which may include hyperboloid shape). The other surface is shaped as a meniscoid modified by the centrifugal force that will transfer some of the liquid precursor from the center toward the periphery. In the case of the convex meniscus, the centrifugal force will flatten the center and create a steeper curvature in the periphery, i.e. increase the spherical aberration of the surface. In the case of a convex meniscus, the centrifugal force will create a meniscus with smaller central radius and modify the surface to approximate something between spheric and parabolic shape. In any case, the hyperbolic aberration cannot be achieved for either a convex or concave meniscoid surface.
Sulc et al. in U.S. Pat. Nos. 4,994,083 and 4,955,903 discloses an intraocular lens with its anterior face protruding forward in order to be in permanent contact with the iris that will center the lens. Both posterior and anterior surfaces may have the shape obtained by rotation of a conical section around of the optical axis (sphere, parabola, hyperbole, ellipse). The iris-contacting part of the lens is a hydrogel with very high water content (at least 70% and advantageously over 90% of water) that is inherently soft and deformable. Therefore, the optical surface deformed by the contact with iris cannot be exactly a conic section surface, but a surface with a variable shape that will depend on the pupil diameter, probably close to a sphere with a somewhat smaller central radius. Namely, this situation is similar to the lens from another reference that achieves decrease in the central diameter by pressing a deformable gel-filled lens against a pupil-like aperture in an iris-like artificial element (Nun in U.S. Pat. No. 7,220,279). Nun '279 does not mention or imply use of hyperboloid optical surfaces. Cummings in U.S. Pat. Publ. Nos. 2007/0129800 and 2008/0269887 discloses a hydraulic accommodating IOL in which a liquid is forced into the internal IOL chamber by action of cilliary apparatus causing thus change of the optical surface and accommodation.
Hong et al. in U.S. Pat. No. 7,350,916 and US Pat. Publ. No. 2006/0244904 disclose an aspheric intraocular lens with at least one optical surface having a spherical aberration in order to compensate the positive spherical aberration of the cornea. The negative spherical aberration is achieved by hyperbolic shape of the optical surface.
Hong et al. in US Pat. Publ. No. 2006/0227286 discloses optimal IOL shape factors for human eyes and defines the optimum lens by a certain range of “shape factors” from −0.5 to +4 (the shape factor being defined by Hong as the ratio of sum of anterior and posterior curvatures to their difference), and at least one of the optical surfaces is advantageously aspherical with conic constant between −76 and −27.
Hong et al. in U.S. Pat. No. 7,350,916 describes an IOL with at least one of the optical surfaces having a negative spherical aberration in a range of about −0.202 microns to about −0.190 microns across the power range.